This invention relates generally to wind turbine energy generation systems and more particularly to methods and apparatus for controlling power generated therefrom and to the wind turbine energy generation systems controlled by such methods and apparatus.
It is a common desire to regulate and/or limit apparent power in wind power plants (hereinafter referred to as “windfarms”). Otherwise, the power generated from the windfarm will vary with the power captured by the blades of each turbine, and that power varies with and the captured power is highly dependent upon instantaneous wind speed. Power can be regulated by, for example, pitching the blades of the wind turbines or rotating the axis of the rotor away from the direction of the wind.
The output of a wind farm can be characterized, at least in part, by an apparent power. The apparent power is the sum of the actual, real power, measured in watts and dissipated through a resistive load, and the reactive power, measured in VARs. The sum of the squares of the real power and of the reactive power is equal to the square of the apparent power. Many uses of windfarms require that the apparent power, i.e., volts times amperes, be limited as a scalar quantity. However, to a wire, the transmission of power corresponds to voltage and amperage. It is often necessary to limit the amperage being sent onto a transmission line, because it is this quantity that results in the heating of components or of the transmission line itself and that causes circuit breakers to trip. Thus, it is sometimes desired to limit apparent power to avoid overload conditions in certain locations along a transmission line or to prevent overloading a piece of equipment rated in Volt-Amperes. If the rated voltage is exceeded, the electrical equipment will break down and spark. If the rated amperage is exceeded, the component will overheat. Thus, it can be useful to limit apparent power and power factor.